1. FIELD OF THE INVENTION
The present invention relates generally to a signal transmitting and receiving method, and more particularly to a method for transmitting signals from a plurality of transmitting units at prescribed intervals.
2. DESCRIPTION OF THE RELATED ART
A remote control system in which various apparatuses are remote-controlled is well-known as an example of a data transmission. In this remote control system, data is transmitted from a transmitting unit placed far apart from an apparatus to the apparatus through a space for the purpose of remote-controlling the apparatus, the transmitted data is received in a receiving unit placed in the apparatus and is decoded, and a signal corresponding to the decode data is transmitted to the apparatus.
In general, the remote control system is operated according to a data transmitting and receiving method in which pieces of transmission data are transmitted from a transmitting unit to a receiving unit at prescribed intervals. In a conventional data transmitting and receiving method, only a single transmission unit is operated. Also, even though a plurality of transmission units are operated the transmission units are not simultaneously operated in the conventional data transmitting and receiving method. In other words, in cases where a plurality of transmitting units placed in a limited area are simultaneously operated or in cases where a plurality of transmission signals overlapped with each other are transmitted from a plurality of transmitting units, it is impossible to decode the transmission signals overlapped with each other in a receiving unit of an apparatus. Therefore, there is a drawback that the apparatus cannot be remote-controlled.
To solve the above drawback, a first conventional data transmitting and receiving method in which a data transmission interval adopted in one transmitting unit differs from that in another transmitting unit is well-known. Also, a second conventional data transmitting and receiving method in which a plurality of transmission frequencies are used according to a frequency multiplexing method is well-known. Also, a conventional polling method in which a two-way communication is performed and a transmission timing at each of a plurality of transmitting units is regulated is well-known.
2.1. PREVIOUSLY PROPOSED ART
An example of the first conventional data transmitting and receiving method is described with reference to FIG. 1.
FIG. 1 shows a timing chart of three series of signals transmitted from three transmitting units according to the first conventional data transmitting and receiving method.
As shown in FIG. 1, a plurality of first signals S1 respectively having a signal width are transmitted from a first transmitting unit at first specific intervals, a plurality of second signals S2 respectively having the same signal width are transmitted from a second transmitting unit at second specific intervals, and a plurality of third signals S3 respectively having the same signal width are transmitted from a third transmitting unit at third specific intervals. The signal width for the first, second and third signals is called a signal transmitting period T, a period in which any first signal S1 is not transmitted is called a first signal transmission pausing period X1, a period in which any second signal S2 is not transmitted is called a second signal transmission pausing period X2, and a period in which any third signal S3 is not transmitted is called a third signal transmission pausing period X3.
In cases where the signal transmission pausing periods X1, X2 and X3 differ from each other, a part of the first signals S1 are not simultaneously transmitted with any second or third signal. That is, the part of the first signals S1 are transmitted to a receiving unit without overlapping with any second or third signal. Also, a part of the second signals S2 are transmitted to the receiving unit without overlapping with any first or second signal, and a part of the third signals S3 are transmitted to the receiving unit without overlapping with any first or second signal.
Accordingly, when the first, second and third signals are continued to be transmitted to the receiving unit for a prescribed period or more, even though the first, second and third transmitting units are simultaneously operated, the first, second and third signals can be reliably transmitted to the receiving unit.
2.2. PROBLEMS TO BE SOLVED BY THE INVENTION
However, because the transmission of the first, second and third signals to the receiving unit is performed when each of the signals is not overlapped with any other signal by chance, the first, second and third signals cannot be reliably transmitted to the receiving unit unless the first, second and third signals are continued to be transmitted to the receiving unit for a prescribed period or more.
Also, in cases where the number of transmitting units is increased, a probability that the signals are simultaneously overlapped with each other is increased, and there is a drawback that a probability that the signals are reliably transmitted to the receiving unit is decreased.
Also, in the second conventional data transmitting and receiving method, because a plurality of frequencies are used, there is a drawback that complicated circuits such as a modulation circuit, a synchronizing circuit and the like and expensive parts are required.
Also, in the third conventional data transmitting and receiving method, because two-way communication is performed between a pair of apparatuses, a transmitting unit and a receiving unit are required for each of the apparatuses. Therefore, there is a drawback that each of the apparatuses is manufactured in a large size and is expensive.